1. Field of the Invention
The present invention relates to a novel method of preparation of a patterned decorative material. In more detail, the invention relates to a method of efficient preparation of a patterned decorative material having embossing on a powder coating layer which has an excellent corrosion resistance, weathering resistance and abrasion resistance, has an excellent durability without formation of craze or loss of luster in the coating even after a prolonged usage and advantageously can be utilized in building materials, electric appliances, furnitures and the like.
2. Prior art
For the purpose of giving atmosphere of high grade, patterned decorative materials excellent in appearance and touch are utilized in building materials such as wall materials and interior materials of buildings, housing materials of electric appliances, furnitures and the like.
Embossing has been known as one of the methods of preparation of such patterned decorative materials. Among such embossed patterned decorative materials, embossed steel plates are manufactured commercially and are utilized in various applications.
The embossed steel plates are usually prepared by coating and baking a layer of plastisol or organosol made of vinyl chloride resins on a steel plate to form a coated steel sheet and embossing the sheet after the baking is finished. The thickness of the coating is generally in the range from 300 to 500 micrometer in the case of a plastisol coating and in the range from 70 to 100 micrometers in the case of an organosol coating (Japanese Patent Publication No. Showa 61-57073).
However, embossed steel plates prepared according to this method have a defect that, because the plastisol or the organosol used for the coating material contains a large amount of plasticizer such as dioctyl phthalate, the coating layer inevitably loses the plasticizer during the prolonged period of utilization and thus formation of craze and loss of luster are unavoidable.
Another method utilized for a similar purpose is that a coating material containing vinyl chloride resin and a thermoplastic resin is coated to varying thickness to form a striped pattern by using a roll so that the resulting coating layer has a decorative pattern by the effect of the variation of thickness (Japanese Patent Publications No. Showa 61-54470 and No. Showa 61-54471). However, a thickness in the range from 150 to 250 micrometers is required in order to have a decorative pattern according to this method and productivity is unavoidably decreased.
On the other hand, the method of powder coating is excellent in processability, gives a coating excellent in weathering resistance and abrasion resistance, is a typical material-saving process and a typical non-hazardous process to the environment and, thus, has been attracting interest during these years. The method is utilized widely in coatings of industrial products like outdoor durable structures such as iron frame materials for buildings, guard rails, fences, street lights and gates, steel furnitures, electric appliances and coatings to replace glass lining.
However, when a coating layer is embossed after the coating layer is completely made on the surface of a substrate by applying a powder coating material on the substrate followed by baking of the coating material, the coating has problems that craze is formed at the edge of the pattern where the thickness of the coating layer varies and that some parts of the coating layer are extremely thin so that the coating is inferior in corrosion resistance during a long period of usage and, as the result, the coating cannot be utilized for a prolonged period. For these reasons, embossed steel plates applied with powder coatings are actually not utilized for practical purposes.